"Jumping the Broom" is a broad African-Amerian family comedy that manages to avoid many of the more predictable cliches of the genre, yet also leaves out the warmth and, too often, the laughs.

A wedding movie that may have viewers rooting for divorce lawyers, “Jumping the Broom” is a broad African-Amerian family comedy that manages to avoid many of the more predictable cliches of the genre, yet also leaves out the warmth and, too often, the laughs. Drawing its title from an antebellum tradition in which slave couples jumped over a broom to signify their commitment to one another, pic boasts a name cast sure to lure underserved black auds, though word of mouth — as well as potential crossover appeal — may be soured by the film’s nasty tone and all-too-tidy resolutions.

As in many wedding movies, there is a Romeo-and-Juliet aspect at the center. Here, it’s purely about class: Sabrina’s family is rich enough to have a block-long house on the water on Martha’s Vineyard; Mrs. Watson (Angela Bassett) is proper, cultured and maybe a little priggish. “They could be … awful,” she says of her pending in-laws.

She has no idea: Jason is a Wall Street “bootstrapper” with a mother, Pam (Loretta Devine), who works in the Post Office and fulfills every stereotype of a government worker. Yes, there’s going to be a collision, but you don’t quite expect it to be this caustic.

Few are better at portraying passive-aggressive than Devine; a single wan smile could collapse empires. But Pam is such an unlikably written character that it’s hard to get past her lack of social graces. Whereas the basic principle of the Romeo-Juliet formula is that each side has its pros and cons, Pam is pure con.

But the pic’s writers don’t offer a lot to grab onto elsewhere, mistaking conflict for character and spleen for heart. Director Salim Akil has everyone acting so earnestly they barely rise above cartoons. Patton, so wonderful in “Precious,” suffers terribly from having a character with no real dimension.

And yet, a couple of the purely comedic satellite characters come close to saving the day: Tasha Smith as Pam’s best friend Shonda, is tart and funny as she tries to fend off a much younger admirer (Romeo Miller) she really doesn’t want to fend off. Also strong is Mike Epps as Jason’s lecherous uncle Willie Earl, who, oddly enough, recalls another salacious Uncle Willie, played by Roland Young, in another wedding movie, “The Philadelphia Story.” The comparison might be utterly irrelevant if they didn’t serve a similar function — adding some sex and innuendo to a movie that desperately needs it: While the pic doesn’t belabor Sabrina’s vow of abstinence, it’s a sitcommy element that doesn’t help matters. Only when her friend Blythe (Meagan Good) starts to stir things up with the wedding’s hunky chef (Gary Dourdan), does the movie manage to generate some real heat and evaporate some of its accumulated bile.